1. Field
The invention is in the field of exhaust systems for automobiles, and more specifically thin exhaust pipes for increased ground clearance on racing cars used on oval tracks such as stock cars.
2. State of the Art
Race cars used in automobile racing are typically constructed such that only a minimal amount of clearance is maintained between the underside of the car and the surface of the roadway or track. This is done to lower the center of gravity of the vehicle so as to improve vehicle handling and resistance to rolling over, and to minimize the drag on the car due to air passing thereunder. Likewise, such race cars typically have very stiff suspension systems which do not allow the vehicle to travel as great a distance up and down nor side-to-side as a standard production car allowing the use of less ground clearance. One of the problems encountered in lowering the race car closer to the race track is providing sufficient clearance for the vehicle exhaust system which is one of the lowest hanging components of a typical car, including race cars.
The problem is particularly acute on cars which race on oval race tracks such as stock cars. The exhaust pipes of such stock cars typically exit toward one or both sides of the car so as to minimize the length of the exhaust pipes to the resulting exhaust gas back pressure which back pressure lowers engine power output and overall engine performance, and to keep the hot exhaust pipes away from the fuel cell so as to minimize the chance of a fuel fire. As such, the minimum ground clearance of the exhaust system typically occurs where the exhaust pipes cross under the longitudinally-extending main frame members of the chassis at the sides of the vehicle. Stock cars typically race on oval tracks in a counter-clockwise rotational direction with centrifugal force causing the body and chassis of the car to lean toward the outside of the turn or toward the right side of the car. Therefore, the ground clearance on the right side of the car is less during cornering and the greatest ground clearance results on the left side of the car during such cornering. Also, banked tracks can induce high downward loads to the suspension system of stock cars requiring additional ground clearance. In an effort to increase the ground clearance of the exhaust system on stock cars, thin profile boom tube exhaust pipes were developed which extend at a rearward, laterally outwardly-directed angle from the secondary exhaust pipes under the main frame members of the chassis. The outlet end of such :boom tube exhaust pipe is typically manufactured in a squared-off or right angle end configuration and trimmed at installation to match exit angle and the side of the particular vehicle.
The construction of prior art boom tube exhaust pipes typically takes several forms. A first type of prior art boom tube includes a thin profile, generally flattened sheet metal body having a pair of spaced, parallel flat upper and lower sheet metal pieces and a pair of elongate, U-shaped cross-section sheet metal side pieces welded to respective side edges of the upper and lower sheet metal pieces so as to form a generally flattened tubular body. The upper and lower sheet metal pieces can be tapered so as to form a laterally tapered body which allows the exhaust gasses to expand while travelling therethrough. The upper and lower sheet metal pieces are typically interconnected by a plurality of short rods welded into staggered mating holes in such upper and lower sheet metal pieces. The rods are an attempt to minimize vibration of the broad upper and lower half shells which vibration can cause increased exhaust gas back pressure, resonance and increased noise, and metal fatigue. The boom tube exhaust pipe further includes a single funnel shaped inlet or a pair thereof which is welded to one end of the generally flattened tubular body to connect with the secondary exhaust pipe or pipes of the vehicle. Such inlets typically comprise a longitudinally split thin walled metal tube, the respective halves of which are partially flattened, more so at one end than the other end, and each longitudinally welded at the edges thereof to a pair of upper and lower tapered flat plates, the narrower edge thereof being adjacent the less-flattened ends of the respective half tubes so as to form a generally funnel shaped inlet with a somewhat flattened circular inlet end and a generally flattened profile outlet end. Alternatively, such inlets can comprise a thin walled metal tube into the respective ends of which are forced appropriately shaped arbors or forms which stretch and form the tube into a somewhat flattened circular shaped inlet end and a generally flattened profile outlet end. Such boom tube exhaust pipe is expensive to manufacture due to the multitude of rods and welding involved and is still prone to metal fatigue due to the increased stresses in the half shells at the respective holes therethrough, and due to the increased brittleness of the metal of the half shells and rods due to the heat applied during welding thereof.
A second type of prior art boom tube exhaust pipe comprises a large diameter, thin walled steel tube which is generally flattened so as to form a thin profile, generally flattened tubular body. The upper and lower portions of the tubular body can be inter-connected by a plurality of rods as explained for the first version prior art boom tube exhaust pipe. A single funnel shaped inlet or a pair thereof of similar construction as that of the first version prior art boom tube is welded to one end of the flattened tubular body to connect with the secondary exhaust pipe or pipes of the vehicle. The tubular body of such boom tube exhaust pipe does not taper outwardly from the inlet end to the outlet end due to fabrication from a tube such that exhaust gasses cannot expand while moving therethrough, causing increased exhaust gas back pressure and suffers from the same disadvantages as the first version prior art boom tube exhaust pipe.
A third type of prior art boom tube takes the form of a rectangular extruded steel tube to which a pair of elongate U-shaped cross-section sheet metal side pieces are welded to the sides thereof to form a thin profile, generally flattened tubular body having three elongate passageways therein. A plurality of exhaust crossover holes are typically drilled or milled through the walls of the tube to allow crossover flow of exhaust gasses between the elongate passageways. A single funnel shaped inlet or a pair thereof of similar construction as that of the first version prior art boom tube is welded to one end of the flattened tubular body to connect the secondary exhaust pipe or pipes of the vehicle to direct the exhaust gasses into the ends of the respective tubes. A plurality of such rectangular tubes (or square tubes) can be welded together side-by-side in place of the single rectangular tube with the sheet metal side pieces welded to the two outermost tubes to form a thin profile, generally flattened tubular body of greater width than using a single rectangular tube. A plurality of exhaust crossover holes are typically drilled or milled through the walls of the tubes to allow crossover flow of exhaust gasses between the elongate passageways. A single funnel shaped inlet or a pair thereof is welded to one end of the flattened tubular body to connect the secondary exhaust pipe or pipes of the vehicle to direct the exhaust gasses into the ends of the respective tubes. While such boom tube exhaust pipe is more fatigue resistant than the sheet metal, the weight thereof is greater, the exhaust gas crossover tubes must typically be drilled or milled rather than less expensive punching thereof, and the body is not tapered such that exhaust gasses cannot expand while traveling therethrough, resulting in increased exhaust gas back pressure.
Such prior art boom tube exhaust pipes can be constructed such that the inlet is at or above a lower plane of the body thereof so as to maximize ground clearance. Likewise, exhaust systems comprising a pair of headers each including a plurality of primary exhaust pipes which connect at one end thereof to the cylinder block of an internal combustion engine at respective exhaust outlet ports thereof and at opposite ends thereof which converge into a single merge collector, a pair of secondary exhaust pipes which connect to the outlet of the respective merge collectors, and one or two boom tube exhaust pipes are used in auto racing. Such exhaust systems can be made and mounted to a race car such that the entire exhaust system, including the inlets of the boom tube exhaust pipes, are at or above the lower plane of the bodies of the boom tube exhaust pipes to maximize ground clearance of the exhaust system.
In my co-pending U.S. patent application Ser. No. 09/392,398 titled xe2x80x9cThin Boom Tube Exhaust Pipes . . .xe2x80x9d filed Sep. 9, 1999, now U.S. Pat. No. 6,283,162, which is hereby incorporated herein by reference, I disclose a flattened single or dual inlet boom tube exhaust pipe for use on race cars, such as stock cars which race on oval tracks, which mounts to the standard exhaust system pipes and to the lower frame or chassis of the car, and which routes exhaust gasses to one or both sides of the car while providing improved ground clearance between the exhaust pipe and the surface of the race track. The construction of the boom tube exhaust pipes comprise single or dual slightly flattened circular inlets which lead exhaust gasses into a flattened profile body constructed of formed sheet metal half shells, with the inlets at or above the lower plane of the body. One or more formed sheet metal structural ribs extend through the body and into the inlets and one or more spacer ribs support the half shells within the body. The boom tube exhaust pipes can be made with internal baffles or spiral acoustic traps so as to also be an acoustic muffler.
The invention comprises a Y-pipe assembly for attachment to the respective ends of a pair of primary exhaust pipes or header assemblies which lead exhaust gasses from the engine of a motor vehicle, and to the inlet of a boom tube exhaust pipe which mounts to the bottom portion of the frame or chassis of the motor vehicle, which Y-pipe assembly and boom tube exhaust pipe provide improved ground clearance. The Y-pipe comprises a first secondary exhaust pipe comprising an inlet portion connectable to one of the header assemblies for receiving exhaust gasses therefrom and a bevelled outlet portion, and a second secondary exhaust pipe comprising an inlet portion connectable to the other of the header assemblies for receiving exhaust gasses therefrom and a bevelled outlet portion. The bevelled outlet portions of the secondary exhaust pipes are affixed together along a respective edge of each thereof so as to merge together with respective centerlines thereof at an oblique angle to a single outlet opening which is connectable to the inlet of the boom tube such as by affixing thereto. Both secondary exhaust pipes are preferably substantially the same length as measured along respective longitudinal centerlines thereof such as by curving one secondary exhaust pipe to lengthen to that of the other secondary exhaust pipe and wherein the included convergence angle of intersection of the centerlines is between about zero and sixty degrees, preferably being as shallow an angle as reasonably possible to fit the particular motor vehicle. This equalization of lengths and relatively shallow convergence angle provides a more evenly timed and balanced flow of exhaust gasses therethrough as pressure pulses of exhaust gasses from respective exhausting engine cylinders alternately flow therethrough with minimal induced turbulence for reduced exhaust back pressure and maximum engine performance. The respective secondary exhaust pipes are typically longitudinally tapered in the vertical direction with the first end portion of the respective secondary exhaust pipes being substantially round in cross-section and radially flared so as to closely fit to the respective header assembly so as to be thinner at the second end portion than the first end portion thereof for improved ground clearance.
The invention further comprises a tubular inlet for a boom tube exhaust pipe of the type which further includes a tubular body of generally flattened shape having a first end with an inlet opening for receiving exhaust gasses and a second end which terminates at an outlet opening for expelling the exhaust gasses into the atmosphere, the boom tube exhaust pipe being for attachment to the outlet end of the Y-pipe or other secondary exhaust pipes attached to an exhaust header assembly which leads exhaust gasses from the engine of a motor vehicle. The tubular inlet is preferably made of sheet metal and includes a first end preferably of a somewhat flattened circular shape for attachment to a comparably configured Y-pipe or other secondary exhaust pipe or pipes and having an inlet opening for receiving exhaust gasses therefrom, the tubular inlet tapering from the first end to a generally flattened second end of mating configuration for attachment to the tubular body for channeling the exhaust gasses from the Y-pipe to the body of the boom tube exhaust pipe. The inlet preferably has a flattened lower surface and includes a pair of sheet metal structural ribs of generally trapezoidal shape as viewed from a respective side thereof disposed in a spaced apart relationship which extend generally longitudinally through the tubular inlet diverging from the first to the second end thereof and which vertically span between and are affixed to the tubular inlet juxtaposed an upper and a lower inside surface of the tubular inlet so as to provide support therebetween. The ribs typically include a plurality of exhaust gas cross-over holes which extend therethrough extend therethrough to allow exhaust gasses to flow therethrough.
The tubular inlet works in conjunction with the Y-pipe to draw exhaust gasses from the engine cylinders by means of the pressure pulses therefrom which flow in a generally alternating timing from the respective engine cylinders, through the headers, through the secondary exhaust pipes of the Y-pipe and into the tubular inlet and the body of the boom tube exhaust pipe. Though not quite as efficient as pure alternate firing cylinder engines such as six cylinder flat opposed engines, the Y-pipe and tubular inlet works to improve the performance of eight cylinder V-block engines, which engines have some consecutive pulses through the same header assemblies. The flow of the alternating pressure pulses are accelerated as they merge in the Y-pipe and pass into the tubular inlet wherein the flow is allowed to expand, and further expand in the body of the boom tube exhaust pipe. As a pressure pulse of exhaust gasses flows through one of the secondary exhaust pipes of the Y-pipe and into the tubular inlet, the inertia of the accelerating flow of exhaust gasses passing the opening thereinto of the other secondary exhaust pipe, a partial vacuum or lower pressure is briefly created within such other secondary exhaust pipe. When the next cylinder exhausts into such other secondary exhaust pipe forming a pressure pulse of exhaust gasses, the flow thereof is accelerated due to the lower pressure therein created by the previous pressure pulse such that more exhaust is removed from the exhausting engine cylinder. This increased removal of exhaust gasses from the cylinders of the engine improves engine performance by allowing space for more fresh fuel/air mixture to enter the cylinder for the next firing of the cylinder. The ribs within the tubular inlet (and within body of the boom tube exhaust pipe) direct the flow and control the expansion of exhaust gasses, with the exhaust gas cross-over holes allowing controlled mixing of the exhaust gasses therebetween for fine tuning of the exhaust flows.
A second version of the tubular inlet comprises a pair of respective inner shells of generally L-shaped cross-section and a pair of respective outer shells of generally U-shaped cross-section, the inner shells each being a single piece of formed sheet metal having a generally flat wall portion of generally trapezoidal shape with one of the ribs dependent therefrom also being of generally trapezoidal shape, the outer shells each being a single piece of formed sheet metal having a pair of spaced apart, generally flat walls of generally trapezoidal shape interconnected by respective curved side wall configuration for attachment such as by being affixed to the tubular body. The beveled outlet portions of the secondary exhaust pipes are affixed together at an oblique angle along a respective edge of each thereof so as to merge together at an oblique angle to a single outlet opening which is of mating configuration so as to be connectable to the first end of the inlet such as by affixing thereto for channeling the exhaust gasses from the secondary exhaust pipe to the body of the boom tube exhaust pipe.
A first version of the tubular inlet comprises a pair of respective upper and lower half shells, each being a single piece of formed sheet metal having a pair of respective generally flat upper and lower wall portions interconnected by a curved side wall portion and a tapered rib portion dependent from one of the wall portions, the half shells which are welded together at a pair of generally longitudinally-extending seams and plug welded at a plurality of generally longitudinally-extending plug weld holes through the wall portion adjacent each of the ribs.
The invention further comprises a Y-pipe and tubular inlet assembly comprising a Y-pipe and a tubular inlet, both being of any of the types described above and affixed together, the Y-pipe being of suitable configuration for attachment to the respective ends of a pair of primary exhaust pipes or header assemblies which lead exhaust gasses from the engine of a motor vehicle, the tubular inlet being for attachment to the tubular body of generally flattened shape of a boom tube exhaust pipe having a first end of suitable configuration with an inlet opening for receiving exhaust gasses and a second end which terminates at an outlet opening for expelling the exhaust gasses into the atmosphere.
The invention further comprises a boom tube exhaust pipe comprising an inlet and a tubular body, the tubular inlet being of any of the types described above and a tubular body being of generally flattened shape of any suitable construction and affixed together, the tubular inlet being of suitable configuration for attachment to the end of a Y-pipe or other secondary exhaust pipes leading exhaust gasses from the engine of a motor vehicle, which boom tube exhaust pipe mounts to the bottom portion of the frame or chassis of the motor vehicle, and which provides improved ground clearance between the exhaust pipe and the surface of the ground. The tubular body typically includes one or more structural ribs which extend generally longitudinally through the tubular body and which vertically spans between and is affixed to the tubular body juxtaposed an upper and a lower inside surface of the tubular body so as to provide support therebetween.
The invention further comprises a Y-pipe and boom tube assembly comprising a Y-pipe and a tubular inlet, and a tubular body, all being of any of the types described above and affixed together, the Y-pipe being of suitable configuration for attachment to the respective ends of a pair of primary exhaust pipes or header assemblies which lead exhaust gasses from the engine of a motor vehicle, and which boom tube exhaust pipe of the Y-pipe and boom tube exhaust pipe assembly mounts to the bottom portion of the frame or chassis of the motor vehicle, and which provides improved ground clearance between the exhaust pipe and the surface of the ground.
The invention further comprises exhaust systems which include the Y-pipe and boom tube exhaust pipe assemblies of the invention, for use on motor vehicles powered by an internal combustion engine having multiple power cylinders at opposite sides thereof, for attachment to the engine of a motor vehicle, which exhaust systems provide improved ground clearance between the exhaust pipe and the surface of the ground. The exhaust systems comprise a Y-pipe and boom tube exhaust pipe of any of the types described above, and a pair of exhaust pipe header assemblies each including a plurality of primary exhaust pipes each connectable at a first end thereof to a respective power cylinder at a respective side of the engine and a merge collector into which respective opposite ends of the primary exhaust pipes are affixed.